First Report of Colletotrichum acutatum Causing Bitter Rot on Apple in Italy

Italy could be considered the main apple-producing country in the European Union. Italian apple (Malus domestica L. Borkh.) production is estimated at approximately 2,100 million tons and encompasses a wide range of varieties, harvested from August to November. Colletotrichum acutatum, which causes severe losses to strawberry production, was a regulated organism for all European countries until 2008, when it was removed from the EPPO quarantine pathogen list because of its wide distribution in strawberry production areas. During the growing season of 2010, fungi were isolated from apple fruits exhibiting bitter rot symptoms after four months of storage in several packinghouses in the Emilia Romagna region. The apples belonged to the ‘Golden Delicious’, ‘Granny Smith’, Pink Lady’ and ‘Crisp Pink’ varieties. Lesions on the fruit surface were circular and 1 to 3 cm in diameter. When lesions enlarged, they became sunken with relatively firm rotten tissues. The fungal fruiting structures, acervuli, were distributed sparsely or densely on old lesions, and under humid conditions, they discharged an orange conidial mass. Conidia observed under a light microscope appeared hyaline and fusiform, sized 8 to 16 x 2.5 to 4 μm, with two pointed ends or one rounded end. The fungal isolates were grown on potato dextrose agar (PDA) plates incubated at 25°C.